Then I would read through here...
Then I would poke around the support discussions here
specifically for the machine you have and the OS you are preparing to install...
I recently purchased Mac OS 10.3 Panther to try out.
I have an iBook Clamshell G3 Indigo. For the benefit of those who are not aware of these machines, it has a 10GB Hard Disk, 128MB of RAM, and a PowerPC G3 at 366MHz. I have doubled its stock RAM which was originally 64MB.
Aside from other upgrades which I will decide on (or not) at the time, will I need to update the firmware? I read somewhere that using old firmware and installing OS 10 will "destroy" the machine.